1. Field of the Invention
The present invention relates to a method of manufacturing a solid-state imaging device, and more particularly to a method of manufacturing a solid-state imaging device in which a light-shielding-film opening is provided on a light receiving surface of each photodiode for constituting a pixel.
2. Description of the Related Art
FIG. 9 is a schematic surface diagram of a CCD-type image sensor which is an example of the solid-state imaging device. In this solid-state imaging device 1, a multiplicity of photodiodes (PDs) 3 are formed on the surface of a semiconductor substrate 2 by being arranged in the form of an array, i.e., in the form of a square lattice in the illustrated example. In addition, a vertical transfer path (VCCD) 4 for receiving and transferring signal charges accumulated by the photodiodes 3 in correspondence with the amounts of light received is provided on a side of each row of the photodiodes. A horizontal transfer path (HCCD) 5 for transferring the signal charges received from the vertical transfer paths 4 to an output stage is provided at a lower side of the semiconductor substrate 2, and an amplifier 6 for outputting voltage value signals corresponding to the amounts of signal charges is provided at the output stage of the horizontal transfer path 5. A light shielding film, a color filter layer, and a microlens layer, which will be described later, are provided on the surface of each photodiode 3.
FIG. 10 is a schematic cross-sectional view taken along line X-X in FIG. 9, and illustrates a section of one photodiode portion. In addition, FIGS. 11 to 15 are diagrams illustrating the procedure for manufacturing this related-art solid-state imaging device. Hereafter, a description will be given of the procedure for manufacturing the related-art solid-state imaging device.
As shown in FIG. 11, a p-well layer 11 is formed in a surface portion of an n-type semiconductor substrate 2, and an n region 12 is formed in a surface portion of the p-well layer 11 to thereby form a photodiode. An embedded channel 4a for constituting a vertical transfer path 4 is formed near a side portion of the n region 12, while a p+ diffusion layer 13 for suppressing a dark current is provided on a surface portion of the n region 12.
The outermost surface of the semiconductor substrate 2 is covered with a gate insulating layer 14, and a transfer electrode 4b for constituting the vertical transfer path 4 is laminated on the embedded channel 4a with the gate insulating layer 14 disposed therebetween. The semiconductor substrate 2 is further covered with an insulating layer 15, and a metallic light shielding film 16 formed of tungsten or the like is laminated thereon. An opening 16a of the light shielding film 16 is open at a position above the light receiving surface of the n region 12.
As shown in FIG. 12, a flattening layer 17 is laminated on the light shielding film 16. Then, as shown in FIG. 13, a through hole 18 which penetrates the flattening layer 17 and the insulating layer 15 is formed by the photolithographic process. This through hole 18 is provided such that its side wall is spaced apart from the side wall of the light shielding film opening 16a. 
Next, as shown in FIG. 14, a high refractive index layer 19 is laminated by using a film forming method such as plasma CVD or by a coating method to fill the through hole 18. As a result, an optical waveguide 20 made of a high refractive index material is formed in the interior of the through hole 18. Then, as shown in FIG. 15, an upwardly convex inner lens 21 formed of a high refractive index material is laminated on the optical waveguide 20. Furthermore, a flattening layer 22, a color filter layer 23, and a top microlens layer 24 are laminated thereon, as shown in FIG. 10.
In the solid-state imaging device manufactured by the above-described manufacturing procedure, the incident light is focused by the microlenses 24 and 21, is guided into-the optical waveguide 20, passes through the interior of the optical waveguide 20, and enters the n region 12. As a result, photoelectric charge is generated and accumulated in the n region 12.
It should be noted that, for example, JP-A-2003-60179, JP-A-2003-224249 and JP-A-2005-116841 are known as relating to the related art.
In solid-state imaging devices in recent years, attempts have been made to increase the number of pixels to millions of pixels or even higher, so that the diameters of the optical waveguide 20 and the light shielding film opening 16a have come to be microfabricated on the order of the wavelength of the incident light.
If the optical waveguide 20 and the light shielding film opening 16a become very fine, new problems which hitherto did not constitute problems emerge. One of them is the loss of light energy due to an evanescent effect. Namely, this is a problem in that when the incident light passes through the interior of the optical waveguide 20, if the evanescent light oozing out from the side wall of the optical waveguide 20 to the outer periphery is shielded by the light shielding film, the loss of energy increases sharply, causing a decline in sensitivity.
To avoid this problem, it suffices if the optical waveguide 20 is formed with a diameter sufficiently smaller than the microfabricated light shielding film opening 16a, but since the optical waveguide 20 itself is formed with a small diameter, the decline in sensitivity still results. In addition, in the related-art manufacturing method, there is no guarantee that the optical waveguide 20 can be formed just in the middle of the light shielding film opening 16a, and there is a possibility that the optical waveguide 20 is offset in the light shielding film opening 16a owing to process variations, and becomes very close to the light shielding film 16.